Editor’s Note: For the next few months, we’ll be sharing weekly lessons that are hard-earned from nearly four decades of garage experiences, exasperations, and general mayhem that either we’ve experienced personally or have been associated with through friends’ miscues. The title intones that most of these errors and screw-ups could have been easily avoided had we been paying attention to the details. So rather than suffer a similar fate, we offer up these lessons learned — the hard way.
Power Steering Bleed
When replacing a steering box, its recommended to bleed the box and eliminate any air in the hydraulic system before starting the engine. This process takes a few minutes but will save time in the long run. It is intended to prevent pushing air into the system with the pump and causing the fluid to foam.
For example, let’s say you just installed a new steering box and filled the pump reservoir, and then started the engine. This pushes high-pressure oil into the box and squeezes the air into the pump where it is instantly turned into foam containing millions of tiny air bubbles. That foam circulates through the system and creates a nasty whine from the pump. It may take hours or even a full day or more to allow the hydraulic system to purge itself of the air in the system. There’s an easy way to prevent this.
The procedure is simple to execute. Make sure all the hydraulic connections are tight and fill the power steering reservoir with power steering fluid. Do not use automatic transmission fluid (ATF) in a power steering system. ATF uses friction modifiers that generally have no place in a power steering system. So it’s best to use a purpose-built power steering fluid.
With the reservoir filled with power steering fluid, raise the front suspension with a jack so the wheels are off the ground and safely supported with jack stands. Now slowly rotate the wheels back and forth to full lock. We like to do this using the wheels but you can do this with the steering wheel. Bubbles will appear in the fluid as the fluid slowly displaces the air in the steering box. This may require refilling the reservoir more than once. Continue to pull the wheels through lock-to-lock until no more air appears in the reservoir. Now you can lower the car to the ground and start the engine. If the fluid in the reservoir falls dramatically, immediately kill the engine and refill the reservoir and bleed the system again with the wheels off the ground and the engine off.
This should complete the bleeding process and allow you to drive the car without the worry of air in the hydraulic system. This process only takes a few minutes to perform and will prevent aeration of the fluid that can take days to dissipate.